The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
A residential or light commercial HVAC (heating, ventilation, or air conditioning) system controls environmental parameters, such as temperature and humidity, of a residence. The HVAC system may include, but is not limited to, components that provide heating, cooling, humidification, and dehumidification. The target values for the environmental parameters, such as a temperature set point, may be specified by a homeowner.
In FIG. 1, a block diagram of an example HVAC system is presented. In this particular example, a forced air system with a gas furnace is shown. Return air is pulled from the residence through a filter 110 by a circulator blower 114. The circulator blower 114, also referred to as a fan, is controlled by a control module 118. The control module 118 receives signals from a thermostat 122. For example only, the thermostat 122 may include one or more temperature set points specified by the homeowner.
The thermostat 122 may direct that the circulator blower 114 be turned on at all times or only when a heat request or cool request is present. The circulator blower 114 may also be turned on at a scheduled time or on demand. In various implementations, the circulator blower 114 can operate at multiple speeds or at any speed within a predetermined range. One or more switching relays (not shown) may be used to control the circulator blower 114 and/or to select a speed of the circulator blower 114.
The thermostat 122 also provides the heat and/or cool requests to the control module 118. When a heat request is made, the control module 118 causes a burner 126 to ignite. Heat from combustion is introduced to the return air provided by the circulator blower 114 in a heat exchanger 130. The heated air is supplied to the residence and is referred to as supply air.
The burner 126 may include a pilot light, which is a small constant flame for igniting the primary flame in the burner 126. Alternatively, an intermittent pilot may be used in which a small flame is first lit prior to igniting the primary flame in the burner 126. A sparker may be used for an intermittent pilot implementation or for direct burner ignition. Another ignition option includes a hot surface igniter, which heats a surface to a high enough temperature that when gas is introduced, the heated surface causes combustion to begin. Fuel for combustion, such as natural gas, may be provided by a gas valve 128.
The products of combustion are exhausted outside of the residence, and an inducer blower 134 may be turned on prior to ignition of the burner 126. The inducer blower 134 provides a draft to remove the products of combustion from the burner 126. The inducer blower 134 may remain running while the burner 126 is operating. In addition, the inducer blower 134 may continue running for a set period of time after the burner 126 turns off. In a high efficiency furnace, the products of combustion may not be hot enough to have sufficient buoyancy to exhaust via conduction. Therefore, the inducer blower 134 creates a draft to exhaust the products of combustion.
A single enclosure, which will be referred to as an air handler unit 208, may include the filter 110, the circulator blower 114, the control module 118, the burner 126, the heat exchanger 130, the inducer blower 134, an expansion valve 188, an evaporator 192, and a condensate pan 196.
In the HVAC system of FIG. 1, a split air conditioning system is also shown. Refrigerant is circulated through a compressor 180, a condenser 184, the expansion valve 188, and the evaporator 192. The evaporator 192 is placed in series with the supply air so that when cooling is desired, the evaporator removes heat from the supply air, thereby cooling the supply air. During cooling, the evaporator 192 is cold, which causes water vapor to condense. This water vapor is collected in the condensate pan 196, which drains or is pumped out.
A control module 200 receives a cool request from the control module 118 and controls the compressor 180 accordingly. The control module 200 also controls a condenser fan 204, which increases heat exchange between the condenser 184 and outside air. In such a split system, the compressor 180, the condenser 184, the control module 200, and the condenser fan 204 are located outside of the residence, often in a single condensing unit 212.
In various implementations, the control module 200 may simply include a run capacitor, a start capacitor, and a contactor or relay. In fact, in certain implementations, the start capacitor may be omitted, such as when a scroll compressor instead of a reciprocating compressor is being used. The compressor 180 may be a variable capacity compressor and may respond to a multiple-level cool request. For example, the cool request may indicate a mid-capacity call for cool or a high-capacity call for cool.
The electrical lines provided to the condensing unit 212 may include a 240 volt mains power line and a 24 volt switched control line. The 24 volt control line may correspond to the cool request shown in FIG. 1. The 24 volt control line controls operation of the contactor. When the control line indicates that the compressor should be on, the contactor contacts close, connecting the 240 volt power supply to the compressor 180. In addition, the contactor may connect the 240 volt power supply to the condenser fan 204. In various implementations, such as when the condensing unit 212 is located in the ground as part of a geothermal system, the condenser fan 204 may be omitted. When the 240 volt mains power supply arrives in two legs, as is common in the U.S., the contactor may have two sets of contacts, and is referred to as a double-pole single-throw switch.
Monitoring of operation of components in the condensing unit 212 and the air handler unit 208 has traditionally been performed by multiple discrete sensors, measuring current individually to each component. For example, a sensor may sense the current drawn by a motor, another sensor measures resistance or current flow of an igniter, and yet another sensor monitors a state of a gas valve. However, the cost of these sensors and the time required for installation has made monitoring cost prohibitive.